class_docstr: A stream operator for aggregating a rolling window of a stream.
  
  Parameters
  ----------
  func : `Callable[[List[float]], float]`
      A function that aggregates a rolling window.
code: def forward(self) -> float:
      rolling = self.inputs[0]
      history = rolling.value
  
      output = (
          np.nan
          if rolling.n - rolling.nan < rolling.min_periods
          else self.func(history)
      )
  
      return output
  
imports: from typing import List, Callable
  import numpy
  from tensortrade.feed.core.base import Stream
  from tensortrade.feed.api.float import Float
label_desc: Use image node_id 2 for calling the RollingNode obj's underlying member method code with example usage: obj.forward() and returns: output